diff --git a/src/main/java/algorithms/sprint5/PyramidSort.java b/src/main/java/algorithms/sprint5/PyramidSort.java
index 37368de..e92fe2d 100644
--- a/src/main/java/algorithms/sprint5/PyramidSort.java
+++ b/src/main/java/algorithms/sprint5/PyramidSort.java
@@ -9,6 +9,8 @@
 //https://contest.yandex.ru/contest/24810/run-report/160623687/
 
 public class PyramidSort {
+    private static final int MAX_PARTICIPANTS = 100_000;
+    private static final int MAX_LOGIN_BYTES = 1_024;
 
     /*
      * Принцип работы алгоритма:
@@ -147,11 +149,21 @@ int nextInt() throws IOException {
             if (c == '-') {
                 sign = -1;
                 c = read();
+                if (c <= ' ') {
+                    throw new NumberFormatException("Expected digit after sign");
+                }
             }
 
             int val = 0;
             while (c > ' ') {
-                val = val * 10 + c - '0';
+                if (c < '0' || c > '9') {
+                    throw new NumberFormatException("Invalid integer input");
+                }
+                int digit = c - '0';
+                if (val > (Integer.MAX_VALUE - digit) / 10) {
+                    throw new NumberFormatException("Integer input is too large");
+                }
+                val = val * 10 + digit;
                 c = read();
             }
             return val * sign;
@@ -170,6 +182,9 @@ String next() throws IOException {
             int n = 0;
 
             while (c > ' ') {
+                if (n == MAX_LOGIN_BYTES) {
+                    throw new IOException("Login token is too long");
+                }
                 if (n == tmp.length) {
                     byte[] next = new byte[tmp.length * 2];
                     System.arraycopy(tmp, 0, next, 0, tmp.length);
@@ -219,6 +234,9 @@ private static void run() throws Exception {
         FastOut out = new FastOut(System.out);
 
         int n = in.nextInt();
+        if (n < 0 || n > MAX_PARTICIPANTS) {
+            throw new IllegalArgumentException("Participant count is out of range");
+        }
         Participant[] a = new Participant[n];
 
         for (int i = 0; i < n; i++) {
diff --git a/src/test/java/algorithms/sprint5/PyramidSortTest.java b/src/test/java/algorithms/sprint5/PyramidSortTest.java
new file mode 100644
index 0000000..cd12398
--- /dev/null
+++ b/src/test/java/algorithms/sprint5/PyramidSortTest.java
@@ -0,0 +1,66 @@
+package algorithms.sprint5;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import java.io.ByteArrayInputStream;
+import java.io.InputStream;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+import java.nio.charset.StandardCharsets;
+
+import org.junit.jupiter.api.Tag;
+import org.junit.jupiter.api.Test;
+
+@Tag("unit")
+class PyramidSortTest {
+
+    @Test
+    void fastInRejectsOverflowingInteger() {
+        PyramidSort.FastIn in = fastIn("2147483648 ");
+
+        assertThrows(NumberFormatException.class, in::nextInt);
+    }
+
+    @Test
+    void fastInRejectsOversizedLoginToken() {
+        PyramidSort.FastIn in = fastIn("a".repeat(1_025) + " ");
+
+        assertThrows(java.io.IOException.class, in::next);
+    }
+
+    @Test
+    void runRejectsNegativeParticipantCountBeforeAllocation() throws Exception {
+        InputStream stdin = System.in;
+        System.setIn(new ByteArrayInputStream("-1\n".getBytes(StandardCharsets.UTF_8)));
+        try {
+            Method run = PyramidSort.class.getDeclaredMethod("run");
+            run.setAccessible(true);
+
+            InvocationTargetException ex = assertThrows(InvocationTargetException.class, () -> run.invoke(null));
+
+            assertEquals(IllegalArgumentException.class, ex.getCause().getClass());
+        } finally {
+            System.setIn(stdin);
+        }
+    }
+
+    @Test
+    void solvePreservesParticipantOrdering() {
+        PyramidSort.Participant[] participants = new PyramidSort.Participant[] {
+                new PyramidSort.Participant("alla", 4, 100),
+                new PyramidSort.Participant("gena", 6, 1000),
+                new PyramidSort.Participant("timofey", 4, 80)
+        };
+
+        PyramidSort.solve(participants);
+
+        assertEquals("gena", participants[0].login);
+        assertEquals("timofey", participants[1].login);
+        assertEquals("alla", participants[2].login);
+    }
+
+    private static PyramidSort.FastIn fastIn(String input) {
+        return new PyramidSort.FastIn(new ByteArrayInputStream(input.getBytes(StandardCharsets.UTF_8)));
+    }
+}